1. Field of the Invention
The present invention relates to an image sensing apparatus having two image sensors, and to an image sensing method.
2. Description of the Related Art
CCD image sensors and CMOS image sensors are widely known and used as solid-state image sensors comprising a semiconductor. A CCD image sensor functions to convert light to signal charge using photoelectric converters placed within pixels, read the signal charge out of all pixels simultaneously and transfer the charge, then convert the transferred signal charge to an electric signal and output the signal as a video signal.
A CMOS image sensor, on the other hand, functions to convert light to signal charge using photoelectric converters placed within pixels, amplify the signal charge pixel by pixel and output the result as a video signal.
Recent consumer-oriented CMOS image sensors have a much higher read-out speed in comparison with CCD image sensors of the same kind. For example, with a prototype image sensing apparatus having a CMOS image sensor, one frame consisting of 6,400,000 pixels can be output 60 times in one second, or one frame consisting of 2,760,000 pixels can be output 180 times in one second. This is disclosed by, e.g., Satoshi Yoshihara (“A 1/1.8″ 6.4M Pixel, 60 Frames/s CMOS Image Sensor with Seamless Mode Change”, IEEE International Solid-State Circuits Conference, February 2006). In accordance with a CMOS image sensor having this function, image sensing with a very large number of pixels at a high frame rate is possible. Accordingly, one frame of an image constituting a moving picture can be provided with the resolution necessary for a still image, and it is possible for the moving picture and still image to be read out seamlessly with no change in the state of resolution.
Again, unlike a CCD image sensor in which image signals from all pixels are read out simultaneously, the CMOS image sensor has a random-access function, i.e., a partial read-out function, in which only some of the pixels in the image sensor are read out partially. For example, in the field of robot vision and vision chips, research is being conducted concerning high-speed vision systems in which the random-access function, namely the partial read-out function, is exploited by taking advantage of the high-speed read-out function and random-access function of the CMOS image sensor. This is disclosed in the specification of Japanese Patent Laid-Open No. 2003-319262 and in Ulrich Muehlmann, et al. (“A New High-Speed CMOS Camera for Real-Time Tracking Applications”, IEEE International Conference on Robotic & amp; Automation, April 2004).
In robot vision, a high spatial resolution and an excellent real-time property are both required in many instances. In this case, on the premise that all pixel information generally will not be necessary for computing an image feature quantity, only the image signal of an area of interest being observed in a frame image is read out, and an area of interest that will be observed in the next frame is updated based upon the information that has been read out. This technique is called an “intelligent pixel-selection function”. Further, in the field of consumer cameras as well, it has been proposed to exploit the random-access function and make the resolution of the image data in an area of interest differ from the resolution of the image data in a peripheral area which is an area other than the area of interest in a frame image. That is, the specification of Japanese Patent Laid-Open No. 2006-60496 discloses reducing the amount of processing and processing time of a moving picture per frame image by treating an area of interest as a high-resolution area and the peripheral area as a low-resolution area.
However, in a case where a large quantity of moving images are dealt with in an image sensing apparatus having an image sensor capable of such high-speed read-out, the higher the sophistication of a task, the more difficult it is to achieve real-time (high-speed) processing consistent with the performance of the image sensor. Furthermore, there is an increase in the cost of the image sensor. In order to process image data at high speed in real-time, reducing the amount of information in the image data is desirable. However, this results in loss of spatial resolution and a decline in information in detailed portions of the image data.